This invention relates to fiber optics level sensor and flow sensor systems and, more particularly to such systems which incorporate a passive, non-electrical sensor head remotely disposed in the sensed environment.
Level and flow sensors which sense the level or flow of a liquid in a vessel, such as a fuel tank, are known and have been widely used in the art. An example of one such level sensor is the vertical float switch disclosed in U.S. Pat. No. 4,066,858, which is assigned to the same assignee as the present invention. This vertical float switch utilizes a sensor head having a pivotally mounted permanent magnet which cooperates with a float in the sensed environment to operate a switch, such as a mercury switch or a microswitch, carried by the magnet bracket. The output of the switch is connected to an external utilization device such a a liquid supply valve and to an external alarm which indicates that the liquid level has reached a given critical level. These devices have the disadvantage in that the electrical connection is established across the switch contacts in the sensor head which is adjacent to the sensed environment and accordingly the device cannot readily be adapted for use in a hazardous environment such as a vessel containing an explosive fuel.
These and other disadvantages are overcome by the present invention wherein there is provided a fiber optics level or flow sensor system which is particularly adapted for use in hazardous environments, process control, and industrial and environmental control applications. The sensor head can be completely non-electrical and is connected to a remote control unit or module by means of at least one fiber optics cable and which is utilized to sense the position of a sensing element such as a float, displacement bob or mechanical vane.